IS OIL ANALYSIS A GOOD DETECTIVE?

Discussion in 'Maintenance Bay' started by Tom Martino, Feb 21, 2021.

  1. Tom Martino

    Tom Martino Filing Flight Plan

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    Recently my Ercoupe's C-85 lost oil prime which resulted in no oil pressure on start-up. Unfortunately, it ran for around 15-minutes - including a run-up, before being noticed. Long story, it was a "friend" warming up plane for oil change and did not notice.

    I know, I know, the engine is ruined, right? Except, I want to add some details ... the operating temperature never got beyond the low end of the green arc. Then, after priming the oil pump, I re-started it and it ran and sounded great (did not fly yet). I then sent the oil in for an analysis, which showed iron, aluminum and tin a bit high ... but lab noted it is not unusual for an engine with under 100 hours (mine had 76 at the time).

    Since then I've changed the oil and filter to run some more before testing the oil again. I haven't flown it since the "incident".

    The engine starts immediately, runs great, no noises, no high temps, no unusual behavior.

    Conventional thought says the engine is shot ... but ... is that a 100% certainty?
     
  2. 3393RP

    3393RP En-Route

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    In those fifteen minutes, your crankshaft turned over 10,000 revolutions without the .0015-.0020 oil film between bearings and the crank that prevent its destruction.

    The only way to find the answer you're looking for is to tear down the engine. Anything short of that and returning the airplane to flight is a risk with likely deadly consequences.
     
  3. MooneyDriver78

    MooneyDriver78 En-Route

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    Depends. I flew a lot and changed the oil about every 35 hours, got no indications that my cam was going bad. Everything was normal. A borescope inspection would be a better diagnostic procedure I think.
     
  4. OneCharlieTango

    OneCharlieTango Pre-takeoff checklist

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    It was still running after 15 minutes with no oil pressure? Normal oil analysis and no metal in the filter? Something doesn’t fit.

    But as for oil analysis, I don’t trust it ever since my Bonanza had a perfect analysis immediately before needing an overhaul.
     
  5. RyanB

    RyanB Administrator Management Council Member PoA Supporter

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    So what was the kicker that revealed a problem?
     
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  6. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

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    I wouldn't think so.
    Good oil pressure? I'd fly it.

    Ain't no A&P. But, I have had a car that was driven a few miles with no oil and lasted for years after that.
     
  7. Flocker

    Flocker Pre-takeoff checklist

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    To answer your initial question "is oil analysis a good detective?", based on my experience I'd say yes.

    I agree with the borescope suggestion. Couldn't hurt to take a look.
     
  8. MBDiagMan

    MBDiagMan En-Route

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    “Likely?”
     
  9. MBDiagMan

    MBDiagMan En-Route

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    A bore scope can not see the bearings and journals. There may very well be minimal damage in the cylinders. Lack of oil pressure has its greatest effect on the crankshaft, camshaft and their bearings. The cylinders are the least of my concern in this case.
     
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  10. William Pete Hodges

    William Pete Hodges Pre-takeoff checklist

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    Are you sure the engine ran 15 minutes without any oil pressure at all? This seems unlikely unless the oil sump was empty or the oil pump had failed. Was the oil sump empty? You didn't say.
    The mostly likely scenario is the oil pressure gauge or sender is bad or unreliable, unless the sump was empty.

    Oil sampling is most valuable when used regularly allowing you to follow a trend. The numbers are in parts per million instead of percent. So an iron reading of 12 is 12 per 1,000,000 or 0.0012%. We are usually talking very small numbers here, so if you get big numbers, even without a trend that is an indication of something bad. You said yourself the lab did not consider those numbers excessive, but you didn't say what they were either.

    If it was me? I'd climb a spiral pattern above the airport to 12000 feet then cruise around in a oval within gliding distance for about 45 minutes, then spiral down and land, I'd pay close attention to the engine noises and Temps. Then I'd drain the oil and cut open the oil filter. If I found a problem or even if I didn't I'd discuss it with an engine builder who knows these engines well. Then based on the engine builder's advice and my own observations I'd decide to fly it or tear it down.

    I have a theory about engines: If it starts good, and runs good, and all indications are good... then it is good.
     
  11. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

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    The small Continentals have issues with oil pump housing wear and a loss of prime.
    Something like that.
    Avoid over water / hostile terrain for a few hours.
     
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  12. MooneyDriver78

    MooneyDriver78 En-Route

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    Engine monitor, even told me which cam node was bad.
     
  13. Grum.Man

    Grum.Man En-Route

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    I wouldn’t assume it’s ruined. There was still oil on the rotating parts for at least a little while. I would fly it keeping good landing spots in reach for 25 hours or so then do another analysis.
     
  14. MooneyDriver78

    MooneyDriver78 En-Route

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    If pull a cylinder you will be able to inspect the internals. Can inspect the lifter surfaces, camshaft nodes, maybe look for play in the crankshaft.
     
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  15. Dan Thomas

    Dan Thomas Final Approach

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    How many of these opinions so far are from experienced mechanics, particularly those who have rebuilt engines that have suffered this very thing?

    I am, and I have. I would not fly it. There's way too much wishful thinking going on here.
     
  16. Mtns2Skies

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  17. murphey

    murphey Touchdown! Greaser! PoA Supporter

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    Oil analysis is one of many tools. Don’t depend on it as the only diagnostic tool.
     
  18. Chip Sylverne

    Chip Sylverne Final Approach

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    Quit with the negative waves, man.
    Is your oil pressure back to the level it was before the incident? Any drop?
    Fresh OH, so the bearings were new, but probably put a lot of wear on them, and didn't do your cam any good.

    15 minutes is a long time. Hell of a break in procedure.
     
  19. Tom Martino

    Tom Martino Filing Flight Plan

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    I appreciate the feedback. All of it. A few notes on this engine. As I said I had 76 hours on this engine, most of the time put on it 12-years ago. I had it in storage. Then, around 5 years ago, I went thru an extensive annual and started flying it again ... but only put around 20 hours on it in last five years. (I mostly fly my helicopter).

    Every once in a great while, if sitting a long time, my engine looses oil prime (not uncommon with small Continental engines). This last time I took the line off the oil pressure gauge and began to pour oil into it. The oil was not flowing freely. Then, blew into the line and felt something break free and the priming oil started flowing thru the line into the engine.

    So, reflecting back to when the engine was run "without oil pressure" indicated on the gauge ... the engine never seized or even slowed down. It never reached any abnormal temps. Is it possible that there was some internal engine oil pressure, but simply was not getting to gauge?

    A word on my oil gauge. It is electronic, a line comes off the engine into a transducer (converts pressure to voltage), then the voltage is interpreted as "pressure" on the electronic gauge. To verify I had not pressure, I temporarily hooked up an analog gauge. The analog gauge confirmed no pressure. I then blew thru the line and added "prime" oil.

    When I re-started, it rant fine and continues to do so on run-ups to full power.
     
  20. William Pete Hodges

    William Pete Hodges Pre-takeoff checklist

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    Talk to an engine builder with experience on this type of engine. Take his advice.
     
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  21. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    Try to run it past Barrett, Cunningham, Western Skyways et at.
    Get at least 2-3 opinions from overhaulers. Even though they may be biased (they want to overhaul engines, after all) and they may want to limit liability by being very conservative.
    Who else would have an experienced answer for you?
    I would like to hear their opinion.
    I think it's possible there is little or no damage. Are you sure that was 15 minutes? That's a long ground run; maybe it was less and you were told or thought you saw 15?
    Anyway:

    Bill Cunningham Powermasters 918-299-0269
    Barrett ask Rhonda 918-835-1089
    WS 970-249-0232
     
  22. Dan Thomas

    Dan Thomas Final Approach

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    15 minutes is a long time, and there was runup power in that time, too, so lots of bearing pressures. Just because somebody ran an engine without oil for some time without it blowing up means nothing. There's always damage, and it's always the bearings that suffer the most. The pistons and rings need very little oil. Those bearings have a lot of pressure on them, and they start to heat up and fail without oil.

    That oil pump will either create pressure or it won't. It has to suck the oil up though about eight inches, and it can't do that if the residual oil has seeped out of the pump's cover plate. It needs that bit of oil to help seal the pump gears against the walls of the pump cavity and against each other. It doesn't pump air worth a hoot. And these engines are so old that new accessory cases aren't available, and since most of them were run with filter screens instead of full-flow filters, they're all scored up, hurting their suction performance even more. If it did manage to suck up some oil, it will go to work properly and generate pressure. There's no halfway about it.

    The last bearings in the engine to get oil are the front ones. The crank front bearing is a wide affair, to support the crank against the bending loads imposed by gyroscopic precession in turns. The front rod journal is much narrower, and if oil is lacking that one gets the oil last. At a minimum I'd be removing that cylinder (#4) and disconnecting the rod to get a look at the bearing and crank journal. One might find that the bearing is burned and the journal discolored, and a micrometer might reveal some loss of metal. Anyone who willingly flies this thing is risking injury or worse. Sure, it's been ground-run and sounds OK, but what will it do at full power for some time in a climb to altitude? Will it keep running after takeoff to a safe altitude? You don't know, and wishful thinking won't make the engine any healthier. What you believe or do not believe does not change the facts.

    I've had two engine failures. I've flown two other airplanes that I later found had REALLY serious structural deficiencies; one had a cracked rear wing spar and the other had its front stabilizer spar broken all the way through. If I had flown them to their design structural limits, inflight failure would have been almost certain. I did a brief prepurchase inspection on an old airplane, and found that the logs recorded an incident where the wind blew it over on its back. I asked the owner if that wing spars had been thoroughly inspected; he just said "they're ok." I advised the buyers to walk away, they did, and that airplane later killed a guy when a cracked spar failed in the pull-up after a buzz job. Being blown over on its back puts all the weight, in negative loading, on the wingtips, exactly the opposite of what the wing was designed to handle. It bends or cracks stuff.

    That sort of thing makes a pilot/mechanic wary of old airplanes and engines, and very careful in inspections. I don't have much patience for pilots that have no maintenance experience making uninformed judgement calls on serious stuff like this.
     
  23. David Megginson

    David Megginson Pattern Altitude

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    Maybe try a managed/advisory service like Savvy, where you pay a fixed fee and they don't stand to benefit from any work you have done. You'll still end up paying a specialist to inspect the engine, but they will help choose the specialist, do the back-and-forth with them, and get other opinions where they think they're needed.
     
  24. 3393RP

    3393RP En-Route

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    In spite of the Panglossian optimism some have posted, the fact remains that engines don't escape damage running without oil pressure for fifteen minutes.
     
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  25. Magman

    Magman Pre-takeoff checklist

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    IMHO Oil Analysis would not be the best tool here.

    IF you really had 0 Oil Pressure you might have also noticed the Lifters clattering.

    Since the Temp is sensing oil temp passing around it in the Screen it would have

    a low reading with no oil moving.

    A good starting point is to drain the oil through a paint strainer.

    Then flush the Sump with a suitable solvent.

    SAVE any metal found .

    This will NOT tell you it is good.

    Can confirm it’s bad though.


    My belief is right now you “just” need a tear-down and probably an O/H.

    If you go ahead and fly it there is a possibility of spinning a Bearing.

    Then you would also need a new Crank and Case.

    Also the specter of a wrecked aircraft and tombstone.
     
  26. Tom Martino

    Tom Martino Filing Flight Plan

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    BTW, the point I was making about the pressure gauge line is that it is a line coming from the case. If it was somehow plugged, the engine could've had pressure but not showing on the gauge. For some reason, when I blew into that line, it was plugged and something broke free and it cleared. I am definitely not trying to talk myself into this engine being "OK". I am a pessimist at heart, when it comes to aviation. I will probably end up pulling the engine and having it overhauled. Or doing an exchange?
     
  27. Magman

    Magman Pre-takeoff checklist

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    Tom

    You should be aware there is a small orifice ( .020 ish) for the OP that could

    possibly become plugged.

    I’ve seen some that are pressed-in that could be dislodged with your application

    of reverse pressure to prime.

    Too bad engines can’t talk!
     
  28. MBDiagMan

    MBDiagMan En-Route

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    My point was that you can’t see the crankshaft journals and bearings unless you split the case. I have yet to see above scope that will fit between journals and bearings, even if severely worn.
     
  29. Chip Sylverne

    Chip Sylverne Final Approach

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    Quit with the negative waves, man.
    Well, yeah, but if I read your post correctly, you had to manually prime the oil pump, so you confirmed no oil was circulating , right?

    You aren't hung yet. As was suggested, pull a couple jugs and look at the furthest rod bearing from the pump. If it shows no evidence of excessive wear, speaking for myself, I wouldn't worry too much. It should look pretty much like new given tsmoh. If it's showing copper or is burnt, well, that speaks for itself too.
    Maybe a little plastiguage might be helpful in determining exactly how much wear took place, if not obvious.
    I would think that after running for 15 mins without lube, including a runup, any damage would be pretty visible at the bearings.

    Just my .02
     
    Last edited: Feb 21, 2021
  30. 455 Bravo Uniform

    455 Bravo Uniform En-Route

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    I didn’t catch if there was an oil filter to cut or just a screen to check. Maybe your answer is there.

    Bad gauge connection?

    This is my opinion (of course, who else’s would it be, duh!): If you had unlimited time and dollars, would you still be looking for an answer that would make you feel better about NOT tearing into it to inspect? If the answer to that is “no”, then you have to ask yourself how many dollars is a bet on your life worth?

    I think you know the answer. It sucks.
     
  31. Daleandee

    Daleandee Cleared for Takeoff

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    Not sure I would fly it but there are several ways to know most of what's going on in the engine before disassembly. Many great ideas mentioned already but one thing I like to watch closely on my engine is the "hot idle oil pressure." Most engines will show good oil pressure when cold or first run of the day. After the engine has been working hard i.e. 30 minutes of cruise flight the oil pressure reading at idle with the engine hot tells a lot. If you notice this number changing it's usually because the bearings are bad and getting worse.

    As noted you can borescope everywhere possible, compression test it, run several oil analysis to see if you are finding metal, cut open the filter and see what's in it, and watch that oil pressure. Again ... if the hot idle oil pressure is changing it means clearances are changing. Now if the cam is destroyed the engine will be coming apart anyway. I have no idea how much you can see of the cam without disassembly.

    It would be very difficult, if not impossible, for me to trust it without a teardown ...
     
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  32. Huckster79

    Huckster79 Pattern Altitude

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    im not sure how i follow a main bearings wear would change my oil pressure at a given oil temp... i can comprehend a hot engine and oil reading lower pressure but cant fathom how that indicates engine bearing health...
     
  33. bbchien

    bbchien Touchdown! Greaser!

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    Oils were normal when my #2 main started shaving. Oils alone will not save you derrière.....
     
  34. Chip Sylverne

    Chip Sylverne Final Approach

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    Quit with the negative waves, man.
    As the bearings wear, the main't and rod oil clearances change. When the oil is hot and less viscous, the wider clearances maintain less pressure.
     
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  35. Huckster79

    Huckster79 Pattern Altitude

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    Im not trying to argue, trying to understand. Isn’t oil pressure all related to pump health and not anything else? Or does it forcefully push it direct through those bearings? So that if they are sloppy the “hole” it’s pushing it through is larger this less pressure?

    I have a mechanical aptitude but no direct education of any sort on the internals of our engines- I’d love to see one in several states of disassembly so I understand more.
     
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  36. Dan Thomas

    Dan Thomas Final Approach

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    The oil has to squeeze through the clearances in various places. It takes pressure to force volume. As the clearances get larger, more oil flows, dropping the pressure. Think of a garden hose: when is the pressure in it at maximum? When the nozzle is shut off. When the nozzle is open a bit, pressure is still high but has fallen a bit. Take that nozzle off and let lots of water flow, and the pressure has fallen way down, since the ability of the faucet and other upstream factors limit the volume of water available. The engine's oil pump is a positive-displacement pump and has a limit to the volume it can pass, so as clearances get bigger and more oil flows, the pressure falls off. The pump can't keep up. Small Continentals have pumps that aren't much more than just big enough to do the job, and bearing wear makes the pressure fall badly. Lycoming's pumps are larger and can pump as much as four times as much as is needed when the engine is new.

    The OP mentioned tin and aluminum in the oil analysis. Tin comes from bearings, aluminum from pistons and from the cam bearings, which are just machined holes in the aluminum crankcase. Crank and cam bearings are highly-loaded things that need constant oil pressure to keep oil between the metals. Bearing loads force the oil out quickly; it's not inclined to stick around. You need a constant flow feeding them. Lifters also run in machined holes in the aluminum.
     
  37. Huckster79

    Huckster79 Pattern Altitude

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    thank you! Certainly makes sense. I guess I never thought much about where and and how it pumps oil. I guess I honestly did t realize that it forced oil through the various bearings. So does it travel through various passages and forced through bearings and sprayed on other things?

    guess I need to do some YouTubing! I have an insatiable desire to learn and understand everything I possibly can. :). Thanks for the help. And good stuff to know sitting behind a c85 every chance I can.
     
  38. Dan Thomas

    Dan Thomas Final Approach

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    The oil, after it's filtered and cooled, goes through passages drilled in the crankcase that pass by the valve lifter bores, holes leading to the main bearings, more holes leading to accessory drive bearings, and finally to the relief valve that releases excess oil to the crankcase to control the pressure. The valve lifters not only get lubricated, but the oil is forced into them where it moves a small piston to take up the valve clearances, and then up the pushrod tubes and into the valve rocker arms, which have holes to take it to the rocker bearing and to the valve tip; it lubricates the interface between the valve and rocker, and some runs down the valve stem to lubricate the guide, though this is very minimal. Some valve stems are sealed to prevent oil getting in there. Most aircraft engines relied on lead in the fuel to do the lubing, at least until better valve guide materials were employed. The main crank bearings get the oil and they get lubricated, but the main journals on the crank have holes drilled in them that take the oil to the connecting rod bearings, and some con rods are also drilled to take the oil up the rod to the piston pin bearing in the rod. The big end of the rod on the crank sometimes has a hole drilled to squirt oil at the bottom of the piston on the other side of the case to cool it. Oil that squeezes past the rod bearings is flung into the cylinders to lubricate the pistons and rings. Very little oil is needed for this, and too much will actually cause the rings to lift well off the cylinder (instead of having just a few molecules' thickness of oil between the cylinder and ring) and the ring will "hydroplane," causing serious oil consumption and sparkplug fouling. You can see that worn rod bearings will pass a lot more oil, and high engine oil consumption is the result.

    upload_2021-2-23_10-18-15.jpeg
     
    Last edited: Feb 23, 2021
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  39. chemgeek

    chemgeek Pattern Altitude

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    Having done my own oil analysis (I have access to both ICP-OES and now TXRF instrumentation that is ideal for measuring trace metals in liquid samples) periodically over the years I would say that it can be informative but of limited usefulness. It's not a panacea for verifying general engine health. Bear in mind that spectral analysis will only tell you about microparticle wear (we are talking about suspended metal particles that are micron-sized). It will not necessarily tell you if you are making bigger bits of metal that could be more urgent. Over the years my oil analysis has often told me things I have found out anyway at annual time or during routine maintenance: my air filter needed changing (higher than usual silicon), I haven't flown in a while (higher than usual iron, probably from minor cylinder corrosion), or I'm getting blowby into the crankcase (high lead readings). While my students and I found the various oil analyses interesting, ultimately, the information was rarely specific enough to make a specific maintenance decision about. When my last engine was reaching end of life, with a worn cam and lifters that were starting to spall, the oil analysis didn't say anything unusual, and the engine was running great other than excessive blowby and an oil-fouled plug in one cylinder which got it pulled for repair. Once the cylinder was pulled, the cam and lifter wear became apparent.

    Spectral oil analysis is kind of like high tech medical imaging: you can find all sorts of interesting things happening that are likely normal and harmless, but if not used in concert with other information, can cause undue and unnecessary anxiety.
     
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  40. Huckster79

    Huckster79 Pattern Altitude

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    thats absolutely fascinating